This invention relates to a pneumatic tire, particularly a high-performance tire capable of effectively enhancing a drainage property without sacrificing the other tire properties.
In the conventional pneumatic tire, particularly so-called high-performance tire reducing an aspect ratio for the purpose of improving a steering stability and the like, a tread pattern is general to be formed by combining a circumferential groove(s) extending along a circumferential direction of the tire with a plurality of slant grooves obliquely extending from the circumferential groove toward an end of a tread.
As a means for more improving a drainage property in such a tire, it is useful to increase a groove area ratio (a negative ratio) by widening a groove width in the circumferential groove or the slant groove.
That is, in the tire having the above tread pattern, the circumferential groove mainly plays a role for discharging water in forward and backward directions of the tire, and the slant groove mainly plays a role for discharging water toward the side of the tire, so that the drainage efficiency in the forward and backward directions and the sideward direction of the tire is enhanced by increasing the negative ratio in these grooves, and hence the improvement of the drainage property as a whole of the tire can be expected.
Moreover, as another means for enhancing the drainage property, it is useful to incline the slant groove at a small angle with respect to the circumferential direction of the tire to form so-called high angle groove and to arrange the slant grooves in a direction of successively entering into a ground contact region from an equator side of the tire toward the respective tread end side to form a directional pattern in a tread portion.
However, all of these means for enhancing the drainage property have naturally a limit from a viewpoint of ensuring the other tire performances.
The inventor has made detailed studies for more enhancing the drainage property without sacrificing other tire performances with respect to the tire wherein at least one circumferential groove and a plurality of slant grooves each obliquely extending from the circumferential groove toward the tread end from are arranged in the tread portion, and obtained the following knowledge.
That is, it has been confirmed that since the circumferential groove promoting the drainage in the forward and backward directions of the tire and the slant groove promoting the drainage in the sideward direction of the tire largely differ in the direction of the drainage, water flowing along the circumferential groove and water flowing along the slant groove collide with each other in an intersect portion between these grooves when water flows together or branches off in such a portion, and hence the disorder is caused in the flowing of water and also the air is entrapped to easily create air bubbles to obstruct the smooth flowing of water and as a result the drainage efficiency tends to lower.
Moreover, it has been confirmed that the drainage mechanism of the tire during the running of the tire under loading changes with the lapse of time, more concretely, the drainage in front of the tire through the circumferential groove is mainly caused just before a part of the tire contacts the ground and the discharge in the sideward direction of the tire through the slant groove rather than the discharge in the forward and backward directions of the tire through the circumferential groove is mainly caused just after such a portion of the tire contacts the ground (inclusive of ground contacting).
It is, therefore, an object of the invention to provide a pneumatic tire, particularly a high-performance tire capable of effectively enhancing the drainage property without sacrificing the other tire performances by arranging pseudo-land portions of an adequate shape in the circumferential groove.
In order to achieve the above object, the pneumatic tire according to the invention lies in that at least one circumferential groove extending along a circumferential direction of the tire and a plurality of slant grooves each opening to the circumferential groove and obliquely extending from such an opening position toward a ground contact end of a tread are arranged in a tread portion, and a pseudo-land portion(s) is formed in the circumferential groove so as to promote a smooth inflow of water flowing in the circumferential groove into the slant groove.
The pseudo-land portion is preferable (1) to be formed such that a cross sectional area thereof is gradually increased toward a given circumferential direction of the tire; (2) to be arranged in the circumferential groove so as to come an end part at a larger side of the cross sectional area of the pseudo-land portion close to the portion of the slant groove opened to the circumferential groove; (3) to be arranged adjacent to a first groove wall of the circumferential groove not opened to the slant groove; (4) to be fixed to the first groove wall or to be arranged separately from the first groove wall; (5) to have such a part closest to the slant groove opening to the circumferential groove that a height measured from a groove bottom of the circumferential groove is within a range of 10-60% of a maximum depth of the circumferential groove; and/or (6) to have such a slant surface that a height is gradually decreased toward the side of the slant groove opening to the circumferential groove.
And also, the slant surface of the pseudo-land portion is preferable (I) to be substantially a flat shape or substantially a curved shape. In addition, when the slant surface is substantially the curved shape, it is preferable that (II) a center of curvature is located outward from the slant surface in a radial direction of the tire or inward from the slant surface in the radial direction of the tire. Furthermore, it is preferable that (III) when the slant surface of the pseudo-land portion is projected onto a ground contact face of the tire, its shape is approximately triangular or trapezoidal; (IV) an oblique side opposite to a basic side successively enters in the ground contact face from a side near to a side wall of a rib-shaped land portion toward a side apart therefrom; (V) when the basic side and the oblique side are projected onto the ground contact face of the tire, the slant surface is isosceles triangular wherein their length are substantially equal to each other and an angle (xcex1) therebetween is within a range of not more than 20xc2x0; (VI) a position of an intersecting point between the basic side and the oblique side is arranged at a lowest side of the slant surface viewing the tire from a front face; (VII) a shape of the oblique side projected onto the ground contact face of the tire is a curved line in which a center of curvature is located outward in a widthwise direction of the tire; and/or (VIII) the basic side of the slant surface is substantially the same height position as a maximum height position of the first groove wall or is located inward from the maximum height position of the first groove wall in the radial direction of the tire.
Furthermore, it is preferable that a pair of circumferential grooves are arranged in the tread portion to form a rib-shaped land portion between these circumferential grooves. The rib-shaped land portion is preferable (i) to be continuously arranged in the circumferential direction of the tire; (ii) to have a center position in the width-wise direction substantially coincident with a pattern center position; and/or (iii) to have a cross angle (xcex8) between the slant surface and a ground contact face of the rib-shaped land portion or a phantom plane arranged in parallel to such a ground contact face within a range of 120-150xc2x0 viewing at a section in the widthwise direction of the tire.
Moreover, it is preferable that a corner part of a land portion defined by the arrangements of the circumferential groove, slant grooves and/or tread end at the side of the equatorial plane of the tire is formed at an acute angle and arranged at a position entering in the ground contact region on the heels of the pseudo-land portion. And also, the corner part is preferable (a) be arranged on the same circumference of the tire as an intersecting point between a section of the pseudo-land portion having a maximum sectional area and the oblique side of the slant surface or on an extension line of the oblique side; (b) to be subjected to a chamfering, more preferably, a chamfering forming a smoothly curved shape; and/or (c) to be connected with the pseudo-land portion.
Furthermore, the slant groove opening to the circumferential groove is preferable to be arranged so as to separate away from the circumferential groove toward a given circumferential direction of the tire. In addition, it is preferable that all of the slant grooves each opening to each of the pair of circumferential grooves and extending toward the respective ground contact end of the tread are arranged in a direction of successively entering in the ground contact face from the side of the circumferential groove toward the side of the ground contact end to thereby form a directional pattern in the tread portion.